Field of the Invention
The present invention relates to an improvement of a bandpass photon detector for inverse photoemission spectroscopy made by combining a low cut filter and a high cut filter, and aims to decrease a fall width at half maximum (FWHM) of the bandpass photon detector for inverse photoemission spectroscopy of the present invention from 0.70 eV at present to about 0.3 eV. In order to cover such defect that if a bandpass width of the photon detector is narrowed, sensitivity is inevitably lowered, it is necessary to improve sensitivity of a photomultiplier consisting of Cu-BeO used as a low cut filter, so that the present invention aims to deposit by vapor deposition potassium chloride (KCl) in a thickness of 500-1000 .ANG. on the first diode of the photomultiplier, so as to improve resolution and detecting sensitivity of a bandpass photon detector, to make high resolution inverse photoemission spectroscopy measurement possible, and to greatly contribute to analysis and evaluation of semiconductors and magnetic materials.